Chemical reaction at interfaces

The ApBq compound layer grows at the expense of diffusion of the B atoms to interface 1 where these atoms then enter into reaction (2.1 0 with the surface A atoms. It is seen that the same partial chemical reaction takes place at the A-ApBq interface in the A ApBq B (see Section 1.2) and A ApBq-ArBs-B heterogeneous systems. The difference between these two systems is that in the former the B atoms which have crossed only the bulk of the ApBq layer enter into the chemical reaction at interface 1, while in the latter the B atoms are to diffuse across the bulks of both layers ArBs and ApBq before entering into this reaction since the only source of the B atoms in both systems is in fact substance B. 

Note that the designations with strokes were only introduced to avoid confusion with the results of Chapter 1. Partial chemical reactions at interface 1 are the same in the A-ApB(j B and A-ApBq-ArBs-B systems, whereas at interface 2 these are different. Therefore, equations (1.6) and (2.51) are identical, while equations (1.21) and (2.52) are different. Note that not only... 

If diffusion of silicon prevails, as in Fig. 4.8, then partial chemical reaction at interface 2 is the same in both couples ... 

Think in terms of a capacitor. With a pure, nonconducting dielectric material there is a constant electric field between plates (see Fig. L3.20). But across a salt solution between nonreactive, nonconducting, ideally bad electrodes (no chemical reactions at interfaces), there is a spatially varying electrostatic double-layer field set up by the electrode walls (see Fig. L3.21). 

The following five chapters deal with problems associated with solid phases, in some cases involving surface and interfacial problems. In Chapter 14, Steele presents a review of physical adsorption investigated by MD techniques. Jiang and Belak describe in Chapter 15 the simulated behavior of thin films confined between walls under the effect of shear. Chapter 16 contains a review by Benjamin of the MD equilibrium and non-equilibrium simulations applied to the study of chemical reactions at interfaces. Chapter 17 by Alper and Politzer presents simulations of solid copper, and methodological differences of these simulations compared to those in the liquid phase are presented. In Chapter 18 Gelten, van Santen, and Jansen discuss the application of a dynamic Monte Carlo method for the treatment of chemical reactions on surfaces with emphasis on catalysis problems. Khakhar in... 

S.S. Dukhln, G. Kretzschmar and R. Miller, Dynamics of Adsorption at Liquid Interfaces, Elsevier (1995). (Although the emphasis is on the kinetics of adsorption, desorption and chemical reactions at interfaces, much information on the measurement and interpretation of interfacicil and surface tensions can be found.)... 

Unresolved problems include overall theory and related experiments on the contribution of chemical reactions at interfaces to the relaxation spectrum for a better theoretical description of surface rheological parameters. As discussed above each chemical reaction is characterised by at least one relaxation time. On the other hand surface rheological properties, for example dilational elasticity, are connected to relaxations taking place at interfaces. 

Yokokawa H (1999) Generalized chemical potential diagram and its applications to chemical reactions at interfaces between dissimilar materials. J Phase Equilib 20(3) 258-287... 

Neutron scattering is used in many different scientific fields. Neutrons can be used to smdy the dynamics of chemical reactions at interfaces for chemical and biochemical engineering, in food science, drug synthesis and healthcare. Neutrons have been used to investigate polymers and to reveal the molecular structure of... 

Yok] Yokokawa, H., Generalized Chemieal Potential Diagram and Its Applieations to Chemical Reactions at Interfaces between Dissimilar Materials , J. Phase Equilib., 20(3), 258-287 (1999) (Phase Relations, Review, 93)... 

Sitzmann E V and Eisenthal K B 1988 Picosecond dynamics of a chemical-reaction at the air-water interface studied by surface second-harmonic generation J. Phys. Chem. 92 4579-80... 

Corrosion as a Chemical Reaction at a Metai/Environment interface... 

Impact tests Such tests reveal the resistance of coatings to deformation and destruction by concentrated sudden stresses. They thus throw considerable light on the integrity of the metal-coating bond. Changes in adhesion through chemical reaction at the paint/metal interface will be reflected in the impact-test values. 

The diffusivity in gases is about 4 orders of magnitude higher than that in liquids, and in gas-liquid reactions the mass transfer resistance is almost exclusively on the liquid side. High solubility of the gas-phase component in the liquid or very fast chemical reaction at the interface can change that somewhat. The Sh-number does not change very much with reactor design, and the gas-liquid contact area determines the mass transfer rate, that is, bubble size and gas holdup will determine reactor efficiency. 

The liquid-liquid interface is not only a boundary plane dividing two immiscible liquid phases, but also a nanoscaled, very thin liquid layer where properties such as cohesive energy, density, electrical potential, dielectric constant, and viscosity are drastically changed along with the axis from one phase to another. The interfacial region was anticipated to cause various specific chemical phenomena not found in bulk liquid phases. The chemical reactions at liquid-liquid interfaces have traditionally been less understood than those at liquid-solid or gas-liquid interfaces, much less than the bulk phases. These circumstances were mainly due to the lack of experimental methods which could measure the amount of adsorbed chemical species and the rate of chemical reaction at the interface [1,2]. Several experimental methods have recently been invented in the field of solvent extraction [3], which have made a significant breakthrough in the study of interfacial reactions. 

Kinetics of chemical reactions at liquid interfaces has often proven difficult to study because they include processes that occur on a variety of time scales [1]. The reactions depend on diffusion of reactants to the interface prior to reaction and diffusion of products away from the interface after the reaction. As a result, relatively little information about the interface dependent kinetic step can be gleaned because this step is usually faster than diffusion. This often leads to diffusion controlled interfacial rates. While often not the rate-determining step in interfacial chemical reactions, the dynamics at the interface still play an important and interesting role in interfacial chemical processes. Chemists interested in interfacial kinetics have devised a variety of complex reaction vessels to eliminate diffusion effects systematically and access the interfacial kinetics. However, deconvolution of two slow bulk diffusion processes to access the desired the fast interfacial kinetics, especially ultrafast processes, is generally not an effective way to measure the fast interfacial dynamics. Thus, methodology to probe the interface specifically has been developed. 

The numbers in the parentheses indicate the phases in which the reactants and the products are soluble. Since X does not dissolve in phase 2 and Y in phase 1, their only possible meeting place is the interface between the two phases, 1 and 2. It is necessary to transport atoms of X and of Y to the interface. The reaction product XY has also to be transported away from the interface. The reaction would otherwise come to a halt due to the accumulation of XY at the interface. Each of these individual processes mentioned may be addressed as kinetic steps and for the reaction cited, these steps are (a) the transfer of X from the bulk of phase 1 to the interface (b) the transfer of Y from the bulk of phase 2 to the interface (c) chemical reaction at the interface and (d) the transfer of XY from the interface into the bulk of phase 1 (say). The steps listed can be grouped into two categories. The steps (a), (b), and (d) are mass transfer processes, while the step (c) is a chemical reaction step. A simpler situation is encountered in many of the reactions in process metallurgy. Phase 1 is a gas... 

The dissolution process, in general, consists of the following chemical reaction at the solid-liquid interface ... 

But within the pH range of natural waters, the dissolution (and precipitation) of carbonate minerals is surface controlled i.e., the rate of dissolution is rate determined by a chemical reaction at the water-mineral interface. Fig. 8.1 gives the data on the dissolution rates of various carbonate minerals in aqueous solutions obtained in careful studies by Chou and Wollast (1989). 

In this overview we discuss recent advances in the study of chemical reactions at the mineral-water interface as we introduce the... 

Any complete mechanistic description of chemical reactions at the oxide-aqueous electrolyte interface must include a description of the electrical double layer. While this fact has been recognized for years, a satisfactory description of the double layer at the oxide-electrolyte interface still does not exist. 

This section and the next are dedicated to the basics of the silicon-electrolyte contact with focus on the electrolyte side of the junction and the electrochemical reactions accompanying charge transfer. The current across a semiconductor-electrolyte junction may be limited by the mass transport in the electrolyte, by the kinetics of the chemical reaction at the interface, or by the charge supply from the electrode. The mass transport in the bulk of the electrolyte again depends on convection as well as diffusion. In a thin electrolyte layer of about a micrometer close to the electrode surface, diffusion becomes dominant The stoichiometry of the basic reactions at the silicon electrode will be presented first, followed by a detailed discussion of the reaction pathways as shown in Figs. 4.1-4.4. 

The abiotic characteristics of aqueous-solid phase interfaces strongly influence chemical/biochemical reactions in the interface microenvironment of aqueous-solid phases. These reactions at interfaces are controlled mainly by biotic activity. Specifically, all aqueous-solid phase microenvironments contain living microorganisms that mediate biochemical transformations. Solid phases (e.g., soil and sediment particles) usually contain billions of microorganisms, with the aqueous phase containing smaller, but still significant, populations [22,33-39]. 

PROGRESS CURVE ANALYSIS REACTION RATEA/ELOCITY CHEMICAL KINETICS Reactions at interfaces,... 

The essential differences between the properties of matter when in bulk and in the colloidal state were first described by Thomas Graham. The study of colloid chemistry involves a consideration of the form and behaviour of a new phase, the interfacial phase, possessiug unique properties. In many systems reactions both physical and chemical are observed which may be attributed to both bulk and interfacial phases. Thus for a proper understanding of colloidal behaviour a knowledge of the properties of surfaces and reactions at interfaces is evidently desirable. 

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